This invention relates to varying physical properties of materials and more particularly to a mechanical technique for controlling viscosity, point velocity and pressure of a fluid through the creation of predetermined dynamic micro-shear, velocity and pressure fields within a fluid.
Fluid processing, particularly control of overall flow behavior, is vital to various industries. For example, how to make plastics melt to flow easily without degradation is the most crucial issue for plastics molding industry. The ability to transport crude oil is not only critical to these companies in that business, but also is critical to the whole society. In modem industry, fluids are extremely diverse in origin and composition, ranging, for example, from fermentation broths and food products to mineral slurries and polymer melts. However, underlying this diversity are certain properties that determine the overall flow behavior. These properties generally include viscosity, pressure, and velocity.
The viscosity of a fluid refers to its resistance to flow, i.e. the xe2x80x9cstickinessxe2x80x9d of the liquid. For instance, honey has a much higher viscosity than water. In general, the lower viscosity a fluid has, the more easily it will flow. Fluid is classified into two categories according to viscosity: Newtonian fluids and non-Newtonian fluids. A Newtonian fluid such as water has constant viscosity under a certain temperature. A non-Newtonian fluid refers to a fluid whose viscosity is variable under a constant temperature. Plastics melt, crude oil and pulp fall into this latter category. Pressure normally includes static pressure and dynamic pressure. Static pressure comes from gravity or external forces while dynamic pressure largely comes from a fluid""s internal velocity inconsistencies. For non-Newtonian fluids, viscosity depends on both temperature and shear or xe2x80x9cfrictionxe2x80x9d, which is influenced by dynamic pressure and thus velocity inconsistency. Although these properties influence each other, different applications pay more attention to some of them versus the rest.
Various conventional fluid processing techniques have been used to control these physical properties to satisfy industry needs. These techniques include using heat and shear for viscosity control, and using a pump for pressure control and also for velocity control. Though these techniques are widely used, they have their limits that they can not address all the needs, sometimes create problems, and are sometimes too expensive to use. These issues leave the door open for new fluid processing technologies.
By way of example, the petroleum industry is a huge industry that controls the lifeline of our society. The petroleum industry is composed of integrated oil companies and oil field equipment and services companies as well as pipeline, refineries and resellers. Due to the high cost of project implementation and competition, technology plays an important role in this industry.
As a result, fluid handling is a major issue in petroleum industry. Crude oils produced from wellbores are normally very viscous, which creates challenges for both oil recovery and oil transportation. To make this kind of oil flow through an oil pipeline, a high pressure has to be applied to the oil which has to be maintained throughout the entire pipeline. This is very costly and very inconvenient. The high viscosity of oil is one of the major reasons that so many pumping stations are required. An effective way to reduce viscosity would significantly reduce cost. In the past, as illustrated by U.S. Pat. No. 4,945,937, various attempts have been made to lower the viscosity of crude oil. Moreover, while this patent refers to the use of ultrasonic energy in such a process, it turns out that a wax crystal modifier must be added. Moreover, just adding energy to a tank does not significantly alter the physical characteristics of the fluid.
Moreover, a large problem for oil pipelines is oil spill caused by erosion. Localized high dynamic pressure is one of the causes of erosion. How to control dynamic pressure and thus prevent or deter severe erosion presently is an open question.
Another challenge comes from recovering viscous oil from oil wells. Some wells are filled with viscous petroleum liquids such as heavy crude oil and bitumen that makes them not pumpable with conventional pumping equipment. The high cost associated with well drilling makes it highly necessary to find new technologies to solve the problem.
As to papermaking, the paper industry is both energy intensive and capital intensive. The industry requires high capital outlays for mills and equipment. As a slowly moving industry, it is characterized by boom-and-bust periods. No company can respond instantly to increased demand, because construction of equipment and facilities takes at least four years to complete. There is thus a need for new technologies in paper industry.
The paper industry is faced with a number of problems and challenges. Pulp is the basic building block of paper and paperboard products. It is predominately made from wood. Wood pulp, like other types of pulp, is manufactured by separating the wood fibers which are held together by a material called lignin. The fibers can be separated by either mechanically tearing them apart or by chemically dissolving them.
Pulp handling, including manufacturing, transporting and processing, is central to the paper manufacturing process. Pulp, with its viscous nature and other properties, requires sophisticated mechanical systems. The current manufacturing system requires large amounts of energy, which are costly and are not necessarily environmentally friendly. Lack of technology innovation makes the industry operate in a non-optimized way. As evidenced by U.S. Pat. Nos. 4,013,506, 5,213,662, 5,705,032, and 5,472,568 in the last 20 years, research has been done on how to handle pulp more efficiently. Still, new technology for pulp handling remains critical, especially with respect to energy and environmental concerns.
Not only are fluid handling efficiencies important to the paper making industry, in the marine field, propulsion and other problems are prevalent. Noise produced by a propeller is one of the sources that expose a submarine to detection. Noise is mainly caused by uneven pressure distribution, which causes a propeller to vibrate in an unwanted fashion. How to control the uneven pressure distribution and thus reduce noise is a challenge in this industry.
Another big concern is that of cavitation. The major problem encountered with cavitation is its violent nature. Upon the collapse of the vapor xe2x80x9ccavitiesxe2x80x9d produced by cavitation a small implosion occurs. These implosions can generate tremendous noise and can be violent enough to damage the blade sections, causing accelerated erosion of the blade surface. As well, the presence of the cavities often changes the performance of the blade section unfavorably. For severe cavitation of a propeller under heavy load, the propeller can become substantially enveloped in cavitation causing thrust breakdown of the propeller and thus loss of thrust. Thrust breakdown is one of the factors that limits the maximum speed of a ship. Eliminating or alleviating the severity of cavitation will not only protect the propeller, but also opens the door for increasing ship speed. Cavitation occurs when the local pressure drops below the fluid vapor pressure. By the very nature of lifting surfaces, low-pressure regions occur on the foil surface that at sufficiently high loads will eventually cavitate. Once again, pressure control remains a question.
In another area, the brewing industry is a very old industry. Competition is intense due to its maturity and globalization, and how to lower manufacturing cost by reducing cycle time is thus important. Typically, the brewing process begins when the malt suppliers soak the barley grain in water, thereby facilitating germination. Then the mill uses steel rollers to crack the grain open before it enters the mash tun. In the mash tun, the malts are mixed with warm water. Thereafter, the result is pumped into a lauter tun, where it is sparged with hot water. This helps extract as much of the sugars from the malt as possible. The conversion of proteins and carbohydrates takes 30-60 minutes but the mashing procedure takes 2-3 hours. Then the base of beer is pumped into the brew kettle and moved to a fermentation cellar where it becomes beer. Fermentation may take several weeks or longer. Particle velocity plays an important role in how long each step will take. If particles are moving fast enough, the reaction can be made quicker and easier. To accelerate this process, control of particle velocity will help to accelerate the brewing process.
As to the plastics molding industry, viscosity plays a pivotal role. Traditionally heat and shear are used for viscosity reduction. These two methods can not always provide the required results. With the increasing acceptance of plastics in various engineering applications, there is a need for technologies that can overcome these problems.
The competitive advantage of the plastic molding industry lies in its ability to create complex geometric parts in a very short cycle time. To do this, molders must quickly force molten plastic into a mold and then rapidly cool it until it solidifies. The extent to which this can be done is largely related to viscosity. In general, the lower a material""s viscosity, the more easily it will fill a mold. The standard means for lowering a polymer""s viscosity is by applying either heat or shear. The effect of heat on viscosity can be seen from a common experience of heating honey to make it thinner. Shear is microscopically equivalent to the friction between molecules. The fact that pulling taffy will make it softer is an example of using shear to reduce viscosity. In a typical manufacturing process, electric heaters are used to control temperature and either an electric or a hydraulic machine is used to introduce shear by applying high pressure on plastics melts.
Unfortunately, with plastics, both methods have drawbacks and limits to their applicability. The problems with heat are a) Heat may cause material degradation; b) Heat can not be used in a mold since the mold must be kept cool; c) Some materials are not sensitive to heat. d) Using heat increases cycle time. Likewise, shear has these problems: a) It may break the molecular bonds and lead to material degradation; b) It requires sophisticated equipment; c) The shear effect happens only in localized small areas in the current manufacturing process.
As exemplified by U.S. Pat. Nos. 5,803,106 and 4,793,954, ultrasonic apparatus has been used to alter the flow rate of melts. However, these systems are not controllable in terms of the energy direction, energy focusing, the waveform of the energy, the amplitude of the energy or frequency, and thus offer only limited advantages. Also the energy injected into the fluid is only at the die orifice making it an extremely localized energy injection.
Another method not often used is to mix the original polymer with low molecular weight material. This usually lowers material strength and impacts end product properties. Due to these limits, there are a number of problems in the plastics molding industry that remain unsolved. Typical problems include: the mold filling problem in which one is unable to fill a mold. Secondly, there are part quality problems involving warping, blushing, material degradation, and melt fracture. There are also process problems involving material burning, and nozzle blocking. Difficulty in processing some large molecular weight materials also has caused problems, as has the incapability of meeting the demands of making large and complex parts. Finally, there is a lack of enough knowledge about viscosity control that makes current mold design provide low yield rates which translate into expense. Most of these problems can ultimately be attributed to high viscosity.
In order to solve the above pressing problems, a system for fluid processing is provided to control shear, point velocity and pressure in either a Newtonian or non-Newtonian fluid. The system includes creation of three fields, namely a dynamic microshear field, a dynamic velocity field and a dynamic pressure field. By dynamic is meant that the fields have time varying characteristics including intensity and distribution of the fields.
In one embodiment, the fields are created by the injection of energy between 1 KHz and 10 MHz into the fluid, with the frequency being controllable, with the amplitude being controllable, with the waveform of the energy being controllable, and with the direction of injection being controlled. Control is achieved by control of the angle at which mechanical energy is delivered, steering and/or focusing of the energy, control of the amplitude of the energy, the waveform of the energy, and frequency of the energy in one embodiment to eliminate standing waves.
By controlling these parameters, the three fields are simultaneously controlled, with the zone of energy being expanded over that described in U.S. Pat. Nos. 5,803,106, and 4,793,954. This zone is called the microshear zone and is controllable to provide a predetermined shear, velocity and pressure profile. The subject system is thus able to control overall fluid behavior by changing the physical properties of the fluid. In one embodiment, energy is injected into a fluid at any angle to the direction of flow assuming the fluid is flowing, with the injected energy A providing a uniform and controllable zone of energy in the fluid at the region of energy injection. In another embodiment, the container itself is a transducer and acts as a processor, where the energy comes from the container itself. In a further embodiment, a phased array is used at the container or fluid conduit for electronically steering and focusing energy to any point within the container. Note that the direction and focusing of the injection of energy is turnable by physically moving a transducer or by the use of a phased array.
More specifically, a system is provided for altering the physical properties of fluids by the controlled injection of energy into the fluid. The system in one embodiment is used for controlling the dynamic pressure of a fluid by injecting the energy. In another embodiment the viscosity of non-Newtonian fluids is controlled by controllably injecting energy into the fluid. In another embodiment, for the plastics industry the injection of acoustic energy is used to delay the onset of crystallization.
Further, as to viscosity reduction, and in contradistinction to the teachings of U.S. Pat. Nos. 4,793,954 and 5,803,106, it has been found that successful results can be achieved by injecting the energy not substantially in the flow direction, e.g. outside of 15xc2x0 of the flow direction. As mentioned above, one feature of the subject invention is the ability to control the physical properties of the fluid by controlling the direction in which the acoustic energy is projected into the fluid. Direction can be controlled either by physically moving the transducer or through the use of a phased array.
When the fluid is composed of long chain molecules, the physical properties are altered by the disentangling of the long chain molecules when the fluid passes through a zone of injected energy. The subject system can thus be utilized anywhere disentangling of long chain molecules is beneficial such as to create lower viscosity, to lower dynamic pressure, and to create laminar flow. In the molding industry, the subject system may be used for delaying crystallization by lowering the crystallization temperature, in some cases by as much as 10 degrees Fahrenheit.
In one embodiment, the energy projected into the long chain molecule provides a microshear zone throughout the material, which shear provides local activation energy at each molecule so that the long chain molecules disentangle and move away from adjacent molecules, thereby straightening the long chain molecules and reorienting them along the flow axis. The result of disentangling the long chain molecules is a reduction in viscosity without addition of heat and a delay of crystallization onset. The injection of energy can affect the nucleation process by delaying the formation of the nuclei and growth of the crystal. Additionally, the frequency of the energy is tunable which is especially useful in molding operations. In one embodiment the acoustic energy in the microshear zone is tunable between 1 KHz and 10 KHz.
The use of the subject invention in the plastics industry provides a good example as to how varying physical properties of the fluid provides beneficial results. However, the example is only for illustrative purposes and the invention is not limited thereto. In order to control the viscosity of the molten material and to alter its crystallization temperature, in the subject invention a microshear field or zone is generated through the coupling of mechanically-generated energy into the apparatus which confines the molten material. For molding applications, the means coupling this mechanically-generated energy couples it either to the barrel, to the runners, or to the mold cavity itself. It is the purpose of the microshear zone to disentangle the long chain polymers, straighten them and thereby dramatically reduce the viscosity of the molten material without the addition of heat so high that it is deleterious to the process. In one embodiment, this energy is injected either transverse to or opposite the flow direction and is tunable in frequency to permit maximization of the particular process.
In one application, a two kilowatt acoustic or subacoustic generator is utilized operating between 1 KHz and 220 KHz, with the generator being frequency tunable. The tuning is adjusted in one embodiment so as to adjust viscosity for a given application such as for the barrel, runner or mold in a molding process so as to tailor the mechanical wave energy to the particular application.
As a result of the coupling of mechanical energy into the long chain polymer, the subject system provides an extended microshear zone throughout the entire volume of polymer in the vicinity of the transducer utilized to connect the generator device to the particular part involved. It has been found that the energy in the microshear zone is imparted to each of the long chain molecules and not in the case of molding just at the walls of the barrel as is the case with the friction-induced energy of the feedscrew. Note that in molding while high shear occurs at the walls of the barrel, the energy of this high shear is not transmitted to all of the long chain polymer molecules. In the subject system mechanical wave energy is imparted to all of the long chain molecules in the vicinity of the mechanical wave generator which alters physical characteristics of the polymer, such as lowering the overall viscosity of the material. Thus, all of the long chain polymers which pass through the microshear zone are disentangled, not just the ones at the wall of the barrel.
Importantly, it has been found that this disentanglement which causes the low viscosity is exhibited throughout the molding process, with the long chain polymers not becoming intertwined for periods of hours after the mechanical wave energy has been imparted to the molten material. Moreover, it has been found that crystallization temperatures of the polymer can be reduced by as much as 10 degrees Fahrenheit.
Thus, in one embodiment, the viscosity reducing system is provided for disentangling long chain polymers utilized in the molding process in which a zone of mechanically generated energy is provided either down stream of the hopper in the barrel utilized ahead of the mold, at the runners for the mold, or at the mold itself, with the mechanically-generated energy transferring a wave into the mold charge to provide a zone of high shear throughout the entire volume of material. The high shear provides activation energies so that the long chain molecules can disentangle and move away from adjacent molecules, thereby straightening the long chain molecules and reorienting them along the flow axis. The result of disentangling the long chain molecules permits reduction of the temperature of the mold charge such that the required viscosity can be achieved without application of additional heat.
Because no additional heat is required to achieve low viscosity the mold can be run colder so that the parts solidify in record time to reduce cycle time for the parts. Moreover, energy is saved. The reduction of the viscosity through the microshear process also permits easy filling of the mold by eliminating the increase in viscosity when a traditional mold charge meets the cold mold. Part quality is improved through the utilization of the microshear zones in which warping, blushing and discoloration due to the reduction in the change in temperature between the melt and the mold. This reduction in temperature change also results in reduced cycle times. Moreover, material degradation of the polymer is greatly reduced through the utilization of the microshear technique in which the prior problem of exceeding setup temperatures for the polymers is eliminated, and in which burning of the polymer from the heat applied to achieve low viscosity is also eliminated. With the subject microshear technique the melt is always kept within the process window, thus eliminating the problem of setting the temperature to the upper limit of the window. Moreover, the subject technique provides uniformity in the viscosity throughout the molding process. The subject process also permits the utilization of high-molecular weight polymers which have better mechanical properties but which are difficult to mold because high-molecular weight materials have higher viscosity""s. Further, molten fracture is eliminated.
Additionally, it has been found that energy well below the ultrasonic range of 10 KHz to 900 KHz provides for significant viscosity reductions. This frequency in one embodiment is achieved through the speed at which mechanical vibrators vibrate which are not restricted to the fixed frequency of ceramics or piezoelectric transducers normally utilized. Moreover, it has been found rather than utilizing a single ultrasonic frequency, it is indeed important to be able to tune the mechanical wave source to provide different frequencies for different applications most notably to eliminate standing waves. Presently, frequency tunable piezoelectric transducers may be employed to provide frequency control.
Note that, the disentanglement of long chain molecules has application not only in the molding industry but also in any area in which viscosity is to be reduced. Moreover the injected energy in the subject invention may be in the flow direction when it is not important that the fluid pressure be controlled. For instance, while in the molding application it is important not to deleteriously affect the pressure of the injected molten material due to the utilization of ultrasonic or other enhancements which provide a forward pressure, in other applications such as food processing or lowering the viscosity of oil, the injected energy is effective not only when it is injected transverse to the flow direction but also slightly ahead of this direction.
Note also that, biological tissues can be completely disrupted by the application of ultrasonic energy. Ultrasonic energy has also found use in the depolymerization for viscosity control of synthetic and natural polymers. It is not however the purpose of the subject invention to break molecules apart as illustrated in U.S. Pat. No. 3,497,005 where ultrasonic energy is in fact utilized to break molecular bonds. Thus in the subject invention the energy injected is far below that which would result in the break up of molecular bonds.